While this seems like a simple question, be warned that it is not! To truly give an answer on the matter of worth delves into how you plan to eat, how much time do you have to spend, and what you're looking at structuring.
Normally, I type a book in response to this question (which we get all the time, and I never mind writing said book
), but I don't have time right now (meeting in 10 minutes...which means I should probably be working...meh).
The gist of it is, if you're planning on dining the way that the plan (whichever one) is structured, then it can be a savings. If you're not, then chances are you're better off without it. For kids, the meal plans are typically good savings in general, as feeding a child on $12-$15 a day is tricky in Disney (assuming their own meals and snacks). Adults, it's a bit trickier. So long as you aim for the higher half of the menus and restaurants for the majority of your meals (TS or QS), you should come out ok.
Here is a reply to a similar question (though, it was only about the
DDP) that may get you started. I'm sure that you can infer similar key points for the QSDP from that list plus what I wrote above. Apologies that I don't have time to type up a custom one for you individually (yes, I really do prefer to do that as people's situations change and that changes the tone of the response), but I suppose I have to do this work thing so I can afford my own trip!